The disclosure of the following priority application is incorporated herein by reference: Japanese Patent Application No. 2001-237662 filed Aug. 6, 2001
1. Field of the Invention
The present invention relates to a focusing type distance measurement apparatus that measures the distance to a target object by transmitting light so as to focus the light at the target object and then receiving the light reflected or scattered from the target object.
2. Description of the Related Art
There are apparatuses that measure distances by using light waves in the related art. In a distance measurement achieved by using light waves, the distance to a target object is determined by transmitting modulated light toward the target object, receiving the light reflected from the target object and detecting the difference between the phases of the modulation signals corresponding to the transmitted light and the received light. A distance measurement apparatus adopting this measurement method may measure the distance to a corner cube (prism) used as the target object by transmitting modulated light toward the corner cube and receiving the light reflected from the corner cube or it may instead measure the distance to the target object which is not a corner cube by causing modulated light to scatter at the surface of the target object and receiving the scattered light. An apparatus that measures distances without using a corner cube is referred to as a non-prism type distance measurement apparatus. When light scattered at the target object is received, the light quantity of the received light flux is very much smaller than the light quantity of the received light flux of the light reflected at a corner cube (approximately 1/1 million). For this reason, a focusing type distance measurement apparatus adopts a configuration that allows measurement light (modulated light) to exit an objective lens toward the target object so as to condense the measurement light flux onto the target object and also allows the scattered light from the target object to be condensed on a light-receiving element via the objective lens, to ensure that a sufficient quantity of light is received. There is a demand for this type of focusing type distance measurement apparatus that also allows the use of a corner cube as the target object.
If the position of the corner cube used as the target object becomes offset or the corner cube vibrates, a collimation position of the focusing type distance measurement apparatus becomes offset from the center of the corner cube. If the measurement light flux enters the corner cube at a position offset from the center, the reflected light exits the corner cube from the position symmetrical to the point of entry at which the measurement light flux entered, relative to the center of the corner cube. This reflected light is transmitted through the objective lens as a light flux originating from a position off the collimation position of the focusing type distance measurement apparatus, i.e., off the optical axis, and forms an image at a position off the optical axis. Since the light-receiving element is normally provided on the optical axis, the quantity of light entering the light-receiving element changes as the corner cube vibrates, causing difficulty in achieving an accurate distance measurement. Such a vibration of the corner cube is particularly problematic in a short distance measurement, i.e., when the distance to the target object is small.
An object of the present invention is to provide a focusing type distance measurement apparatus that facilitates measurement of a short distance (several tens of meters or less) performed by using a corner cube.
A focusing type distance measurement apparatus according to a first aspect of the present invention comprises a collimating optical system that collimates the light from a target object, a light-transmitting optical system that transmits a measurement light flux to the target object, a focusing optical system that condenses the measurement light flux onto the target object, a light-receiving optical system that receives a reflected light flux reflected from the target object via the focusing optical system and a deflecting optical member that changes the state in which the measurement light flux is condensed on the target object.
The focusing type distance measurement apparatus in the first aspect of the present invention may further include an operating member that outputs an operation signal for performing distance measurement by using a prism as the target object and a control circuit that implements control on the deflecting optical member to achieve a first state at the deflecting optical member so as to change the state in which the measurement light flux is condensed when the following conditions are present; the operation signal has been output through the operating member and the light reception level indicating the quantity of the reflected light flux received at the light-receiving optical system is equal to or lower than a predetermined value or the light reception level manifests a significant change and implements control on the reflecting optical member to achieve a second state so as not to change the state in which the measurement light flux is condensed when the conditions are not present.
A focusing type distance measurement apparatus in a second aspect of the present invention, achieved by replacing the deflecting optical member that changes the state in which the measurement light flux is condensed on the target object with a deflecting light optical member that changes the state in which the reflected light flux received at the light-receiving optical system is condensed, further includes an operating member that outputs an operation signal for performing distance measurement by using a prism as the target object and a control circuit that implements control on the deflecting optical member achieve a first state so as to change the state in which the measurement light flux is condensed when the following conditions are present; the operation signal has been output through the operating member and the light reception level indicating the quantity of the reflected light flux received at the light-receiving optical system is equal to or lower than a predetermined value or the light reception level manifests a significant change and implements control on the deflecting optical member to achieve a second state so as not to change the state in which the measurement light flux is condensed when the conditions are not present.
A focusing type distance measurement apparatus in a third aspect of the present invention, achieved by replacing the deflecting optical member that changes the state in which the measurement light flux is condensed on the target object with a deflecting optical member that changes the state in which a reflected light flux received at the light-receiving optical system is condensed, further includes a control circuit that implements control on the deflecting optical member so as not to change the state in which the reflected light flux is condensed if the light reception level indicating the quantity of the reflected light flux received at the light-receiving optical system exceeds a predetermined value.
A focusing type distance measurement apparatus in a fourth aspect of the present invention, achieved by replacing the deflecting optical member that changes the state in which the measurement light flux is condensed on the target object with a deflecting optical member that changes the state in which a reflected light flux received at the light-receiving optical system is condensed, further includes an operating member that outputs an operation signal for performing a short distance measurement by using a prism as the target object and a control circuit that implements control on the deflecting optical member to achieve a first state so as to change the state in which the measurement light flux is condensed when the operation signal has been output through the operating member and implements control on the deflecting optical member to achieve a second state so as not to change the state in which the measurement of light flux is condensed when the operation signal has not been output.
A focusing type distance measurement apparatus in a fifth aspect of the present invention comprises a collimating optical system that collimates the light from a target object, a light-transmitting optical system that transmits a measurement light flux to the target object, a focusing optical system that condenses the measurement light flux onto the target object, a light-receiving optical system that receives a reflected light flux reflected from the target object via the focusing optical system, an internal light path through which the light flux transmitted from a light source at the light-transmitting optical system is guided to a light-receiving unit in the light-receiving optical system within the measurement apparatus instead of allowing the light flux to be transmitted toward the target object, an external light path through which the measurement light flux transmitted from the light-transmitting optical system is guided to the target object and the reflected light flux reflected from the target object is guided to the light-receiving optical system and a switching shutter that selects either the internal light path or the external light path for the light flux transmitted from the light source to be guided through, with a deflecting optical member that changes the state in which the measurement light flux is condensed on the target object provided at the switching shutter.
The focusing type distance measurement apparatus in the fifth aspect of the present invention may further include a first operating member that outputs an operation signal to enable distance measurement by using a prism as the target object and a control circuit that implements control on the switching shutter so as to change the state in which the measurement light flux is condensed when the operation signal has been output through the first operating member and the light reception level indicating the quantity of the reflected light flux received at the light-receiving optical system is equal to or lower than a predetermined value or the light reception level manifests a significant change.
Alternatively, the focusing type distance measurement apparatus in the fifth aspect of the present invention may further include a second operating member that outputs an operation signal for performing a short distance measurement by using a prism as the target object and a control circuit that implements control on the switching shutter so as to change the state in which the measurement light flux is condensed when the operation signal has been output from the second operating member.
In the focusing type distance measurement apparatuses described above, a light attenuator that adjusts the light reception level of the light received at the light-receiving optical system may be provided at the deflecting optical member. It is desirable to adjust the light reception level through the light attenuator when the deflecting optical member is in the second state. Such a deflecting optical member may include a plurality of light transmittance adjustment areas provided along the circumference of a rotating plate and a diffusion area where the light flux is diffused provided along the direction in which the plurality of light transmittance adjustment areas are arranged. In this case, the control circuit may include a motor in order to rotate the rotating plate. In addition, the control circuit inserts the diffusion area at a measurement light path when the deflecting optical member is in the first state and inserts one of the plurality of light transmittance adjustment areas in the measurement light path when the deflecting optical member is in the second state.
The deflecting optical member in a focusing type distance measurement apparatus according to the present invention may be constituted of an optical member that achieves a diffusing function or an optical member that achieves a refracting function.